The present invention relates to a corrugated tube which is covered over a wire harness (a flux of electric wires) and a process for producing the same. More particularly, the present invention relates to the corrugated tube of an overlapping type in which a slit is made in an axial direction of the corrugated tube, and a lap portion provided so as to project from one of end edges of the slit is lapped on the other end edge at an inner peripheral side thereof, and the process for producing the same.
Generally, the corrugated tube which is used for bundling and protecting transmission and distribution wires for electronic appliances or wire harnesses in a motor vehicle includes a tube made of synthetic resin and provided with spiral or annular ridge portions which are continuously formed on an outer periphery of the tube so as to impart flexibility to the tube.
This corrugated tube for protecting the wire harness or the like is provided with a slit in an axial direction so that the wire harness can be easily taken into or out from the corrugated tube.
However, when the corrugated tube of this type is bent along a wiring path to be arranged, the slit may be partially opened near a middle part of a bent area, and there is such an anxiety that not only the wire harness which is contained therein may protrude from an opening in the slit requiring a trouble of inserting it again, but also the wire harness may get caught by edges formed on both sides of the slit, incurring damage on an insulating coating.
Under the circumstances, the corrugated tube is usually wrapped with an insulating tape on an outer peripheral face thereof to prevent the slit from being opened. However, it has been a problem that a work for wrapping this tape has been annoying.
In order to solve such a problem of the corrugated tube, there have been proposed various corrugated tubes of the overlapping type in which the slit would not be opened to form an opening even when the tube is bent.
A corrugated tube 1 of the overlapping type as shown in FIGS. 12 and 13 includes a slit 5 which is formed in an axial direction of a tubular body 3, and a plate-like lap portion 8 which is provided so as to project from one of end edges on both sides of the slit 5 and lapped on the other end edge at an inner peripheral side thereof, so that a wire harness W inside the tube may not be exposed even when the tube is bent, thus eliminating the tape wrapping work.
Further, in the corrugated tube 1, the lap portion 8 to be lapped on the other end edge at the inner peripheral side is in a shape of a plate, and its end edge is rectilinear along the axial direction.
As the results, when the slit 5 is opened to receive the wire harness W, the wire harness W is not likely to get caught by the end edge of the lap portion 8, and a work for containing the harness can be conducted smoothly. Moreover, the end edge of the lap portion 8 which is lapped on the inner peripheral face of the corrugated tube 1 will not damage an insulating coating of the wire harness W contained therein.
On occasion of producing the corrugated tube 1 as described above, a tube-like molten resin is extruded from a die, as a first step, into a tubular mold having a desired molding face on its inner face, Then, corrugation of the above mentioned molding face is transferred to the tube-like molten resin by applying air pressure to the tube from inside or by evacuating the tube from outside, and thus, the long size tubular body 3 is continuously produced.
As the results, in the tubular body 3, there are integrally molded a plate-like portion 7 extending in the axial direction, and a bellows portion 9 having circular ridge portions 10 which are bulgingly formed on an outer peripheral face of the tubular body except the plate-like portion 7 and continuously provided in the axial direction.
As the next step, by forming the rectilinear slit 5 by cutting the plate-like portion 7 in the axial direction thereof, the overlap portion 8 in a plate-like shape is projectingly formed at one of end edges on both sides of the slit 5, as shown in FIG. 13.
Then, by heating for molding the tubular body 3 in such a manner that the lap portion 8 may be lapped on the other end edge at the inner peripheral side, the corrugated tube 1 of the overlapping type is produced.
However, in the corrugated tube 1 as described above, at the same time as the lap portion 8 is formed in a plate-like shape, there are inevitably formed end walls 12 and 14 at respective circumferential end portions of the ridge portions 10 which are opposed to each other on both sides of the slit 5.
Consequently, there has been a problem that when the corrugated tube 1 is bent along the wiring path, the corrugated tube 1 itself becomes difficult to be bent, and the wiring operation may be hindered. Particularly, as shown in FIG. 15, when the corrugated tube 1 is forced to be bent in a direction in which the lap portion 8 lies inwardly (in a bending direction in which the tube is downwardly protruded in FIG. 15), flexibility of the tube is not favorable due to strong repulsive forces of the end walls 12 which are parallel to the bending direction and have high rigidity.